Temperature controlled showerhead

ABSTRACT

A temperature controlled showerhead for chemical vapor deposition (CVD) chambers enhances heat dissipation to enable accurate temperature control with an electric heater. Heat dissipates by conduction through a showerhead stem and fluid passageway and radiation from a back plate. A temperature control system includes one or more temperature controlled showerheads in a CVD chamber with fluid passageways serially connected to a heat exchanger.

FIELD OF THE INVENTION

The present invention pertains to apparatus and systems for depositingfilms on a substrate. Specifically, the invention pertains to a chemicalvapor deposition (CVD) apparatus for injecting gases into a reactionchamber. Even more specifically, the invention pertains to a temperaturecontrolled showerhead and its temperature control system.

BACKGROUND

CVD showerhead reactors employ a perforated or porous planar surface todispense reactant and carrier gases as uniformly as possible over asecond parallel planar surface. This configuration can be used forcontinuous batch processing of multiple substrates or processing ofsingle round wafers. Wafers are generally heated to a processtemperature at which the reactant gases react and deposit a film on thewafer surface.

Showerhead reactors, or parallel-plate reactors, lend themselves toimplementation of plasma-enhanced processes, e.g., plasma-enhancedchemical vapor deposition (PECVD). In most PECVD reactors the top andbottom electrodes are about the same size. The wafer electrode may be asubstrate support and be grounded and the showerhead may have RF powerapplied. Bias RF power may be applied to the substrate support. Theapplied RF in the showerhead may necessitate insulating sections in thegas supply system to avoid creating a parasitic discharge in the gasfeed lines to the chamber. RF power may be applied through the substratesupport electrode, while the showerhead may be grounded.

Wafer-to-wafer uniformity may be affected by varying reactiontemperature from wafer-to-wafer: process conditions, clean cycles,idling time, and change in emissivity of the showerhead components overtime can all affect the substrate or wafer as well as the gas reactiontemperature. Although after a number of wafers in continuous batchprocessing the showerheads eventually reach an equilibrium temperature,these factors can affect the equilibrium temperature or the number ofdeposition cycles before the equilibrium temperature is reached. Also,in a multiple station chamber, showerhead temperature may vary fromstation to station. For example, the cool incoming wafers at station 1may lead to a progressive cooling of the showerhead. The thermal cycleof showerheads may also create particles from coatings on the showerheadhaving different coefficients of thermal expansion from the showerheaditself.

It is therefore desirable to accurately control the temperature of eachshowerhead in a chamber to create a manufacturing-worthy equipment withbest wafer-to-wafer uniformity. The showerhead should be designedwithout creating particles and be manufacturable at the lowest costwithout increasing footprint or reducing throughput while maintaininggood wafer-to-wafer uniformity.

SUMMARY OF THE INVENTION

A temperature controlled CVD showerhead and temperature control systemwith enhanced heat dissipation enable accurate and stable temperaturecontrol with fast response. Accurate temperature control reduceswafer-to-wafer non-uniformity within continuous batch processing andfrom batch to batch. The enhanced heat dissipation and heater enablequick recovery to the temperature set point when changes in theoperating environment perturb the system. Increased heat dissipation isachieved by increased conduction through the showerhead stem, additionalconvective cooling using a fluid in a fluid passageway and increasedradiation from a back plate. The temperature control system alsoincludes a heat exchanger that serially cools the convective coolingfluid flowing in the showerhead fluid passageway. In addition, theshowerhead temperature may provide an additional parameter for processoptimization.

In one aspect, the present invention pertains to a temperaturecontrolled CVD showerhead that includes a stem with a convective coolingfluid passageway, a back plate thermally coupled to the stem, a heaterphysically attached to the back plate, a face plate thermally coupled tothe back plate, and a temperature sensor for measuring a temperature ofthe face plate. The temperature sensor may be a thermocouple attached tothe face plate. A non-contact method for temperature measurement, basedon infra-red radiation, fluorescence or pyrometry may also be employed.The back plate may be made of aluminum or an alloy of aluminum. Theexternal surface of the back plate may be coated with a material toincrease emissivity. The coating may be anodized aluminum. The heatermay be an electrical resistance heater and may be embedded in the backplate.

The stem houses a channel through which reactant and carrier gases flowto the face plate, where the gases are distributed through holes orperforations in the face plate. A baffle plate or some otherdistribution device may be located between the end of the gas channeland the face plate to help distribute the gas evenly. The stem alsohouses a convective cooling fluid passageway through which cooling fluidmay flow to cool the showerhead. The fluid passageway is constructed sothat it is isolated from the reactant channel in the stem carryingreactant and carrier gases to the showerhead. The convective coolingfluid enters the stem at an inlet and may exit the stem through one ormore exit channels. In the stem, the inlet or the outlet channel or bothchannels of the passageway may follow a helical path or some othertortuous path designed for conductive heat transfer between the fluidand the surface. The cooling fluid may be clean dry air (CDA), argon,helium, nitrogen, hydrogen, or a mixture of these. Though not preferred,water and oil based liquid coolant may be used as the convective coolingfluid. Particularly, the CDA may be supplied by fab facilities at apressure of about 50-100 psi. The CDA may also be cooled by a heatexchanger connected to more than one showerhead serially. Serial coolingmeans that the CDA may be supplied to various showerheads withintermediate cooling by the heat exchanger. For example, the CDA may besupplied to a first showerhead, cooled by the heat exchanger, suppliedto a second showerhead, cooled by the heat exchanger, supplied to athird showerhead, cooled by the heat exchanger, supplied to a fourthshowerhead, cooled by the heat exchanger, and exhausted. Thisarrangement minimizes the amount of air used and also ensures a lowtemperature of the exhaust, eliminating safety hazards.

The face plate contains holes or perforations through which gasreactants flow to the wafer. The face plate may have variousconfiguration of hole patterns of difference sizes. The face plate maybe removably attached to the back plate so as to facilitate cleaning orchanging hole patterns. The temperature of the face plate may bemeasured by a thermocouple in physical and thermal contact with the faceplate, or by other means that are less susceptible to RF interferences,such as optical thermometry. If a thermocouple is used, it may beconnected to the face plate through a standoff between the back plateand the face plate and through the stem. A radio frequency (RF) filtermay be electrically coupled to the thermocouple to reduce or eliminateinterference in the temperature signal from the applied RF to theshowerhead.

An RF filter may be also electrically coupled to the heater. One or bothof the heater and the thermocouple may be isolated from RF power ofcertain frequency used during deposition. A controller may be coupled tothe thermocouple and the heater to maintain desired temperature at theface plate.

In another aspect, the present invention pertains to a temperaturecontrol system for controlling one or more showerhead temperatures in aCVD chamber. The system includes a CVD chamber and a cooling system. TheCVD chamber includes one or more temperature controlled showerheads.Each showerhead includes a stem, a back plate, a face plate, and athermocouple for measuring the temperature of the face plate. The stemincludes a convective cooling fluid passageway and is thermally coupledto the back plate, which is thermally coupled to the face plate. Thecooling system is connected to the convective cooling fluid passagewaysin each showerhead to serial flow cooling fluid through each showerheadand through the heat exchanger in between showerheads. The coolingsystem may include a liquid cooled heat exchanger and connections to theconvective cooling fluid passageways. The temperature control system mayalso include a controller coupled to the thermocouple and a heaterphysically attached to the back plate.

The convective cooling fluid may be clean dry air (CDA), argon, helium,nitrogen, hydrogen, or a combination of these. The convective coolingfluid may be delivered via a fab facilities connection and may be CDA.The CDA may be delivered at a pressure of about 50-100 psi and ambienttemperature to the first showerhead stem. The CDA may be serially cooledbetween cooling different showerheads, which may or may not be in thesame process chamber on the same tool. One heat exchanger may be used tocool showerheads in more than one chamber for more than one tool. TheCDA may be finally exhausted at ambient pressure and/or ambienttemperature after a last cooling. The liquid coolant in the heatexchanger may be facilities water or another liquid coolant. The heatexchanger may be a cast metal block having embedded coolant line andconvective cooling fluid lines. The cast metal material may be aluminum.The cooling system may also include one or more bypass loops configuredto isolate one or more showerheads from the cooling system. The coolingsystem may also include flow modulators, coupled to the controller, toregulate or control the flowrate of cooling fluids into each showerheadso as to control the amount of cooling. In some embodiments, the CVDchamber may also include a chamber top that has a high-emissivitycoating. The coating may be on the inside surface of the chamber top andmay be anodized aluminum.

In yet another aspect, the present invention pertains to a temperaturecontrol system for controlling CVD showerhead temperature. The systemincludes cooling means thermally coupled to the showerhead; heatingmeans thermally coupled to the showerhead; temperature sensing meansthermally coupled a face of the showerhead; RF filtering meanselectrically coupled to the temperature sensing means and heating means;and, controlling means for controlling temperature. The system may alsoinclude radiative cooling means and convective cooling means.

In one aspect, the present invention pertains to a temperaturecontrolled CVD showerhead that includes a stem with a convective coolingfluid passageway, a back plate thermally coupled to the stem, and a faceplate thermally coupled to the back plate. The convective cooling fluidpassageway may be designed such that cooling fluid exiting thepassageway would be at the same temperature as the showerhead. Theshowerhead apparatus may also include a temperature sensor for measuringthe exit cooling fluid temperature that is outside of the plasma RFinterference range. The temperature sensor may be a thermocouple or anon-contact method for temperature measurement, based on infra-redradiation, fluorescence or pyrometry. The back plate may be made ofaluminum or an alloy of aluminum. The external surface of the back platemay be coated with a material to increase emissivity. The coating may beanodized aluminum. In some embodiment, a heater may be attached to theback plate, which may be an electrical resistance heater and may beembedded in the back plate.

In another aspect, the present invention pertains to a temperaturecontrol system for controlling showerhead temperatures in a CVD chamber.The system may include a CVD chamber with one or more temperaturecontrolled showerheads, a cooling system fluidly coupled to theconvective cooling fluid passageways, and a controller. Each showerheadmay include a stem having a convective fluid passageway, a back platethermally coupled to the stem, and a face plate thermally coupled to theback plate. The cooling system may include inlets and outlets to theconvective cooling fluid passageways, a liquid cooled heat exchanger,flow modulators, and a temperature sensor thermally coupled to aconvective cooling fluid exiting the stem. The heat exchanger may removeheat from the convective cooling fluid that flows serially through thepassageways of the one more showerheads and is intermediately cooled bythe heat exchanger. The flow modulators may control the flow rate of theconvective cooling fluid to each showerhead based on information fromthe controller. The temperature sensor may measure the temperature ofthe fluid exiting a showerhead so that the controller may determine atemperature of the face plate. The controller may be coupled to the flowmodulator and the temperature sensor so as to determine and control theface plate temperature. In some cases, a heater may be attached to theback plate and coupled to the controller to provide heating.

These and other features and advantages of the invention will bedescribed in more detail below with reference to the associateddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of showerhead temperatures in a four station chamberover time.

FIG. 2A is a graph of silicon nitride spacer thickness deposited atvarious showerhead temperatures.

FIG. 2B is a graph of film stress for silicon nitride spacer depositedat various showerhead temperatures.

FIGS. 3A and 3B are cross section schematics of a temperature controlledshowerhead in accordance with an embodiment of the present invention.

FIG. 4 is a schematic of a cooling system in accordance with anembodiment of the present invention.

FIG. 5 is a schematic of a temperature control system in accordance withan embodiment of the present invention.

FIG. 6 is a schematic of one embodiment of RF filters to reduce oreliminate RF noise.

FIG. 7 is a plot of showerhead temperatures measured using a temperaturecontrolled showerhead in accordance with the present invention.

FIG. 8A is a plot showing TEOS film thickness over 100 wafers with fourdifferent starting conditions using a standard showerhead. FIG. 8B is aplot showing the TEOS film thickness over 100 wafers with the same fourstarting conditions using temperature controlled showerheads.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS Introduction

In the following detailed description of the present invention, numerousspecific embodiments are set forth in order to provide a thoroughunderstanding of the invention. However, as will be apparent to thoseskilled in the art, the present invention may be practiced without thesespecific details or by using alternate elements or processes. In otherinstances well-known processes, procedures and components have not beendescribed in detail so as not to unnecessarily obscure aspects of thepresent invention.

In this application, the terms “substrate” and “wafer” will be usedinterchangeably. The following detailed description assumes theinvention is implemented on semiconductor processing equipment. However,the invention is not so limited. The apparatus may be utilized toprocess work pieces of various shapes, sizes, and materials. In additionto semiconductor wafers, other work pieces that may take advantage ofthis invention include various articles such as display face planesprinted circuit boards and the like.

Showerhead temperatures drift over time and affects deposition reactionin terms of reaction rates and film properties. FIG. 1 is a graph of 4showerhead temperatures over a 50 wafer run without any temperaturecontrol, i.e., no heating or cooling. Four showerheads in a four-stationchamber are plotted over a 50 wafer run for about 4000 seconds. Thestation 1 showerhead corresponds to line 102; station 2 to line 104;station 3 to line 106; and, station 4 to line 108. As time goes on, thetemperature in stations 2-4 increases until it reaches a steady statetemperature at about 3700 seconds. The plasma condition is plotted as astep function at line 110. Initially, the plasma remains on in a dummydeposition mode to warm up the showerheads and after about 10 minutes,the wafers processing started. In station 1, the temperature started todecrease gradually after wafer processing started because each incomingwafer at station 1 cools the chamber components, including theshowerhead, as the wafer warms up to the process temperature. Thus thetemperature curves in subsequent stations are progressively higher.Station 2 showerhead is cooler than station 3 showerhead because theincoming wafer to station 2 is cooler than the incoming wafer to station3. For all stations, the showerhead temperature reached an equilibriumtemperature after some time.

FIG. 1 shows that a wafer being processed in a multi-station chamberwould experience a different showerhead temperature at each station.Thus when the showerhead temperature affects the film propertydeposited, each layer deposited on the wafer would have somewhatdifferent properties. One example of a CVD process that is sensitive toshowerhead temperature is the silicon nitride spacer. Another example ofa CVD process that is sensitive to showerhead temperature istetraethylorthosilicate (TEOS).

FIG. 2A shows the film thickness deposited under different showerheadtemperatures. All other process parameters being equal, more film isdeposited at higher showerhead temperatures. Thus the film thicknessdeposited at the beginning of a wafer run, e.g., after some idle time orchamber clean, would be less than the film thickness deposited after theshowerhead temperature has reached equilibrium. Depending on the film,such thickness difference may or may not have an impact in theperformance of the final device manufactured. FIG. 2B shows theshowerhead temperature on a silicon nitride spacer film property—itsstress. As the showerhead temperature increases, the stress decreases.Deposited film stress, especially at the transistor level, may have abig impact on device performance. Thus a desired stress may be achievedby manipulating showerhead temperature. The ability to controlshowerhead temperature would provide another process parameter withwhich to achieve desired film properties and reduce wafer-to-wafervariations (non-uniformity) in deposition thickness and film properties.

Temperature Controlled Showerhead

A temperature controlled showerhead improves wafer-to-wafer uniformityboth for bulk film and individual sub-layers, increases throughput byeliminating non-processing delays, reduces particles by reducing oreliminating thermal cycling, and adds a valuable process parameter forfine-tuning film properties. The film wafer-to-wafer uniformity isimproved because temperature varies less over a continuous batch ofwafers (both within a batch and one batch to another and is independentof the tool condition). This reduces difference in film propertiesbetween the first wafer in a batch when the showerheads are cold and thelast wafer in a batch when the showerheads have reached equilibriumtemperature. By controlling all showerheads in a chamber to be at thesame temperature, the film property uniformity in different sub-layersis also improved. Non-processing time, e.g., dummy deposition time toheat the showerhead, may be eliminated, thus increasing throughput.Thermal cycling may be reduced because the showerhead temperature may bemaintained while the station is idle or being cleaned, instead ofallowing the showerhead to cool. The reduction in thermal cycling wouldreduce the effect of different thermal expansion coefficients betweenchamber components and coatings on the components and thereby reduceparticles. As discussed above, for some CVD processes, desired filmproperties may be achieved by controlling the showerhead temperaturewith other process parameters. For silicon nitride spacers with highstress, for example, low showerhead temperature is desirable.

There are generally two main types of CVD showerheads: the chandeliertype and the flush mount. The chandelier showerheads have a stemattached to the top of the chamber on one end and the face plate on theother end, resembling a chandelier. A part of the stem may protrude thechamber top to enable connection of gas lines and RF power. The flushmount showerheads are integrated into the top of a chamber and do nothave a stem. The present invention pertains to a temperature controlledchandelier type showerhead.

To control temperature, heat is added or removed based on the showerheadtemperature. The showerhead temperature increases when the plasma is on,because (1) charged particles collide with the showerhead to impartenergy, (2) the applied RF energy is coupled to the showerhead, and/or(3) external heat is intentionally added by, for example, electricalenergy from an electrical heater. The showerhead temperature decreaseswhen cooler material enters the chamber, e.g., reactant gases at lowertemperature or wafers at ambient temperature, when heat is removed byconduction, e.g., heat conduction through the showerhead stem materialup to the chamber ceiling, and by radiation from the showerheadsurfaces. Some of these thermal events occur as a part of normal chamberoperation, and others may be used to control showerhead temperature.

FIGS. 3A and 3B are cross-section schematics of a showerhead inaccordance with an embodiment of the present invention. Referring toFIG. 3A, the showerhead 300 includes a stem 304, a back plate 306, and aface plate 310. The stem 304 may be divided into an upper and a lowersection, which may have different diameters. In one embodiment, theupper stem has a diameter of about 1.5 to 2 inches, preferably about1.75 inches. The lower stem diameter is about 2 to 2.5 inches,preferably about 2.25 inches. The face plate diameter may be slightlylarger and comparable to the wafer size. For example, for a 300 mm (12inch) processing chamber the face plate diameter may be about 13 inches.The face plate and back plate may each have a thickness of about 0.25 to0.5 inches. In one embodiment, the back plate is about 0.5 inches thick,and the face plate is about three eighths of an inch. Reactant gases areintroduced through gas inlet channel 302 in the showerhead stem 304,flow past the back plate 306 and enter the manifold area 308 between theback plate 306 and the face plate 310. A baffle 312 distributes thegases evenly throughout the manifold area 308. Volume of the manifoldarea is defined by the gap between the back plate and the face plate.The gap may be about 0.5 to 1 inch, preferably about 0.75 inch. Thegases enter the processing area through perforations or holes (notshown) in the face plate 310 to cause a deposition on the surface of awafer. In some cases, the face plate 310 is removably attached to theback plate 306 so that the perforation/hole configuration may be easilychanged and the face plate cleaned.

A heater 314 may be thermally attached to the back plate 306. The heater314 may be an electrical heater and may be embedded in the back plate306. The heater may be attached by a vacuum brazing process. The heatercoil 314 is controlled by heater wires 316 that are connected to thecoil through the stem. Because the showerhead is subjected to high RFenergy during chamber operation, all or part of the heater is insulatedand isolated from the RF. The RF isolation may be accomplished throughan EMI/RFI filter or any other commercially available RF isolationdevice. In some embodiments, the heater is not used.

FIG. 3B shows a slightly different cross section of the showerhead toemphasize other elements. A thermocouple 318 is in thermal contact withface plate 310 to measure the face plate temperature. The thermocouple318 is connected from the upper stem through a standoff 320 between theback plate 306 and face plate 310. Similar to the heater wire andelements, the thermocouple is also insulated and isolated from the RF.The RF isolation may be accomplished through an RF trap at a frequencyand an RF filter at another frequency. In other embodiments, othertemperature sensing devices may be used to measure the temperature ofthe face plate. Particularly, a non-contact temperature sensor may beused. Examples include pyrometry, fluorescence-based thermometry andinfrared thermometry.

The temperature controlled showerhead enhances heat removal byconduction, convection and radiation. Heat is conducted away through theshowerhead stem itself, which is connected to a chamber top. The stemdiameter may be designed to maximize conductive heat loss to the chambertop. Heat is also removed by convection through cooling fluids flowingin a convective cooling fluid passageway in the stem 304. The embodimentin FIG. 3B includes a cooling fluid inlet 322, into which coolingfluids, e.g., clean dry air (CDA), argon, helium, nitrogen, hydrogen, ora mixture of these, may be flowed. The fluid may follow a helical pathdown the stem. The helical path is shown in FIG. 3B through openings 324of the convective cooling fluid passageway. The cooling fluid may exitthe stem through one or more cooling fluid exit channels 326. In oneembodiment, two cooling fluid exit channels are provided. Although theexample here uses a helical passageway and two exit channels, oneskilled in the art may design another tortuous passageway to effectivelytransfer heat from the showerhead to the cooling fluid.

The fluid cooling channels may be designed so that the exiting fluid iscompletely heated up to the temperature of the showerhead stem. Becausethe faceplate temperature and stem temperature are correlated, it ispossible to deduce the faceplate temperature by measuring thetemperature of the exiting fluid. The exiting fluid temperature may bemeasured away from the electromagnetic interference caused by the RF.This design may avoid the use of a thermocouple inside the showerheadand its associated RF filtering circuitry.

In another scenario, the cooling fluid may further be modulated tocontrol the amount of cooling. A feedback loop based on the exitingfluid temperature may increase or decrease the flow to change the amountof cooling. This cooling may be in addition to or instead of heat on theback plate. For less demanding applications, the cooing alone may beused to control the showerhead temperature; and, the heater elements andRF isolation devices may be omitted. For more demanding application, themodulation of cooling fluid is an additional parameter to control theshowerhead temperature.

In addition to conduction and convection, heat may radiate away from theshowerhead from the back plate. To improve radiative cooling, theexternal surface of the back plate may be coated with a high emissivitymaterial. For example, the coating may be anodized aluminum. Theradiation may be absorbed by the top of the chamber. The chamber top mayalso be treated with a high emissivity material to increase radiativeheat transfer. The inside surface of the chamber top may be coated withanodized aluminum. The chamber top may be cooled independently, e.g.,with cooling water lines.

The conductive and radiative heat removal keeps the showerhead at lowenough temperatures whereby the electrical heater can accurately heat itback. Without the heat removal, the showerhead temperature would remainhigh and uncontrollable. The heat removal creates headroom fortemperature control. In one embodiment, the heat removal keeps theshowerhead temperature below about 200° C. The heater is a simple coilaround the perimeter of the back plate because most of the heat transferbetween the face and back plate is around the perimeter. Better thermalcontact between the showerhead and back plate also improves temperaturecontrol because conductive heat transfer, and thus heat loss through thestem, is enhanced.

Cooling System

A cooling system connected to one or more showerhead stems cools theconvective cooling fluid that flows through each showerhead stem. Thecooling system includes a liquid cooled heat exchanger and connectionsto the showerheads. FIG. 4 is schematic of a cooling system inaccordance with one embodiment of the present invention. In thisembodiment, a heat exchanger 401 is connected to four showerheads 411,413, 415, and 417. The convective cooling fluid flows serially througheach showerhead and a compartment of the heat exchanger 401. Theconvective cooling fluid enters the system at inlet 409 where it entersthe first showerhead stem. After flowing through one showerhead, theconvective cooling fluid is cooled by a liquid coolant in the heatexchanger before flowing through the next showerhead. After the lastcooling through a last compartment in the heat exchanger, the convectivecooling fluid is exhausted from the cooling system at outlet 411. Theconvective cooling fluid may be clean dry air (CDA), argon, helium,nitrogen, hydrogen, or a combination of one or more of these. In oneembodiment, the convective cooling fluid is facilities provided CDA at afacilities pressure. A different flow rate may be required for differentfacilities pressures. For example, at facilities pressure of 80 psi, 100standard liters per minute (slm) of CDA may be used. The exhaust may beat about or slightly above ambient temperature and pressure. Although anopen system is shown where the convective cooling fluid does not returnto the system, the concept of serial flow through the showerhead andintermediate cooling through one heat exchanger also may be implementedwith a closed system.

In some embodiments, exiting cooling fluid temperature from theshowerhead is measured and used to determine the showerhead temperature.Temperature sensor 441, 443, 445, and 447 may be thermally coupled tothe exiting cooling fluid and yet be outside the range of RFinterference. This configuration would eliminate the need for an RFfiltering device. As discussed above, the convective cooling passagewaysmay be designed so that the exiting cooling fluid temperature is thesame as that of the showerhead stem. One skilled in the art would thenbe able to devise algorithms to correlate measured exiting fluidtemperatures to showerhead temperatures knowing thermal properties ofthe various components.

In certain embodiments, the showerhead may not include a heater attachedto the back plate. The showerhead temperature increases duringprocessing, preheating, and remote plasma cleaning. In theseembodiments, active cooling from the cooing fluid may be used to controlshowerhead temperature. Control valves 421, 423, 425, and 427 controlsthe flow of cooling fluids to the showerhead based on input from thecontroller. The cooling fluid either flows to the showerhead stem or isdiverted in a by-pass loop 431, 433, 435, or 437. More or less coolingmay be accomplished based on the flow of cooling fluids to theshowerhead. An active cooling only design may be appropriate in certainless demanding applications where the range of acceptable showerheadtemperatures is larger. In these embodiments, the showerhead temperaturemay be determined based on the exit cooling fluid temperature or bemeasured at the showerhead through a contact thermocouple or through anon-contact thermal sensing means.

In one embodiment, four showerheads and four compartments are shown inFIG. 4, but the cooling system may be designed with another number ofshowerheads and compartments. In some cases, the cooling system mayserve to cool the showerheads for more than one semiconductor processingtool. If each semiconductor processing tool has one multi-stationchamber with four stations each, a cooling system having 8 compartmentsconnecting to 8 showerheads may be designed to serve 2 tools. Somesemiconductor processing tools may have more than one multistationchamber. In that case a cooling system may be designed to serve all theshowerheads in more than one chamber on a single tool. If a fourcompartment heat exchanger is used on a tool having more than onefour-station chamber, more than one heat exchanger per tool may be used.

In some cases one or more of the showerhead may be bypassed forconvective cooling fluid flow altogether. Thus each showerheadconnection may also include a bypass loop with corresponding valves. Forcertain processes, not every station may be configured to depositmaterial onto the wafer or require a temperature controlled showerhead.In that case the bypass loop may be used at station 4.

The liquid coolant for the heat exchanger 401 enters the system at inlet405 and follows a coolant path 403 before it exits the system at outlet407. Although only one loop is shown for coolant path 403, the coolantpath may consist of many loops depending on the diameter of the coolantpath, heat transfer required, the coolant temperature at the inlet, andany coolant temperature requirements at the exit. The liquid coolant maybe water or any other type of known liquid coolant, e.g., Freon. In oneembodiment, the liquid coolant is facilities delivered water. Afterexiting the heat exchanger, the liquid coolant may or may not be treatedfurther before being released, for example, into the drain. For example,the facilities delivered water as the liquid coolant may be exhausteddirectly. However, if other liquid coolant is used, the coolant may becompressed and recirculated back into the heat exchanger, creating aclosed-loop coolant system.

Different designs of the heat exchanger 401 may be utilized. FIG. 4shows a cross-flow heat exchanger where the currents run approximatelyperpendicular to each other. However, counter-flow or parallel-flow heatexchangers may be used. One skilled in the art would be able to design aheat exchanger with enough surface area to cause desired heat transfer.In certain embodiments, the heat exchanger 401 may be a cast metalenclosing the liquid coolant and convective cooling fluid piping. Themetal may be aluminum or other metal with desired heat transfercharacteristics. The cast metal design allows for a compact heatexchanger with little footprint or space requirement.

Temperature Control System

The showerhead temperature control system includes one or moreshowerheads, the cooling system, and controllers for controlling thetemperature of each showerhead. FIG. 5 depicts the major components ofthe temperature control system as it relates to one showerhead. Notethat showerhead graphic in this figure includes the attachment parts tothe chamber top. Convective cooling fluid flows from component 502 intothe showerhead stem where it is heated in the process of cooling theshowerhead, and exits to the heat exchanger 506. In some embodiments,the cooling fluid flow into the showerhead is modulated by a controlvalve or other flow modulator 522. By modulating the flow, the coolingprovided by the cooling fluid may be increased or decreased.

From the heat exchanger 506, as discussed above, the convective coolingfluid may be flowed to another component, such as 504. If the showerheadis configured as the first station in a chamber, then component 502 maybe the facilities air and component 504 may be another showerhead, suchas station showerhead. If the showerhead is not configured as the firststation, then component 502 and 506 may be the same component, theliquid cooled heat exchanger as discussed above. Note that this coolingloop may not have a feed back loop where more or less cooling may beadjusted. The simple design merely cools the showerhead enough such thatthe electric heater 518 may accurately heat the showerhead to a certaintemperature.

Thermocouple 510 is in physical contact with the face plate, asdiscussed above. Thermocouple 510 is connected to a RF isolation device512 to remove the effect of RF applied on the showerhead as an electrodefrom the thermocouple signal. Typically, the RF applied in a PECVD hastwo frequency components, a high frequency (e.g., 13.56 MHz) trap and alow frequency (e.g., 400 kHz). The RF isolation device may include oneor more filters. In one embodiment, the RF isolation device includes ahigh frequency and a low frequency filter. Without RF isolation, it isbelieved that the thermocouple measurement would not be useful becausethe RF interference would be too great.

A schematic of a possible configuration of the RF isolation device isshown in FIG. 6. The thermocouple 510/601 is surrounded by a stainlesssteel sheath. This sheath is wound to a coil 603 in parallel to acapacitor 605. The coil as an inductor and the capacitor forms a tankcircuit which blocks the 13.56 MHz signal. The coil may have aninductance of about 1 microhenry, and capacitor 605 may have acapacitance of about 85 pf (picofarads). Remaining 13.56 MHz RF isshorted to ground 609 with the second capacitor 607, which may have acapacitance of about 10000 pf. Trapping the high frequency with thesheath also blocks the RF in the thermocouple wires embedded in thissheath. The 400 kHz frequency is not blocked by the 603/605 filter anddue to its lower frequency not shorted to ground by the capacitor 607.So at the end of the 13.56 MHz filter there is still 400 kHz noise thatis subsequently filtered out by the low frequency filter 611. In onedesign, the low frequency filter may be a two-stage low pass filter.Both stages may be a LC design similar to the high frequency filter.Please note that the low frequency filter may be connected directly tothe thermocouple wires, but the high frequency filter may be connectedto the sheath only.

Referring again to FIG. 5. the heater element 518 is connected to its RFisolation device 508. RF isolation device 508 may be an RF filter orother available device to isolate the heater electrical signals from theeffects of the RF applied. The temperature controller 516 reads thetemperature information from the thermocouple 510 through the isolationdevice 512, and adjusts input to the heater 518 through the RF isolationdevice 508 in a feed back loop.

In another embodiment, the exit cooling fluid temperature may bemeasured by a temperature sensing device 520 that is outside of therange of RF interference. In this embodiment, no RF filter is requiredfor the temperature sensing device 520. The controller may correlate theexit cooling fluid temperature to a showerhead temperature.

The temperature controller 516 may also takes feed forward informationfrom component 514. The feed forward information may be that the timeperiod until the plasma turns on. In some cases the feed forwardinformation may also include other predictable events that affect theshowerhead temperature such as wafer processing with cold wafers, gasflow into the showerhead. The controller may increase the heater inputin anticipation of a cooling event, e.g., chamber purge, or decrease theheater input in anticipation of a heating event, e.g., plasma “on.” Thecontroller may also increase the cooling by increasing cooling fluidflow in anticipation of a heating event or decrease the cooling bydecreasing cooling fluid flow in anticipation of a cooling event.

Various combinations of the input and output components may be used indifferent controlling schemes. For example, active cooling (modulatingcooling fluid flow) may be used with active heating (heater in the backplate) to accurately control showerhead temperature. The showerheadtemperature may be measured directly from a thermocouple attached to theface plate, or determined indirectly from the exiting cooling fluidtemperature. In some cases, only active cooling or only active heatingmay be included in the control system. Still other inputs may beincluded, such as temperature sensing of the cooling fluid at the inletto accurately determine the heat removed from the showerhead.

In certain embodiments, the temperature controller may be integratedwith the system controller. In those cases component 514 would not beseparated from controller 516.

EXPERIMENTAL

A showerhead temperature control system was implemented in accordancewith the present invention. The control system implemented included thetemperature controlled showerheads as discussed above and a controllerthat uses only feed back (thermocouple only) input. The showerheadtemperatures for a four-station chamber were measured over a 50 waferrun and plotted in FIG. 7. Temperatures for each showerhead, four inall, are plotted on separate curves. The set point was 260° C.Temperature measured for station 1 is noted as line 701. Temperaturemeasured for stations 2-4 are very close to each other and noted aslines 703. Just like FIG. 1, the plasma condition is plotted also as astep function at 705.

The difference in showerhead temperatures as compared to FIG. 1 wherethe heater is off and temperature is not controlled is dramatic. Duringthe dummy deposition up to about 1800 seconds, the showerheadtemperature behaved similar to that of FIG. 1. The temperatures quicklystabilized after wafer deposition started, at about time 1800 seconds.At least for showerheads in stations 2-4, the temperature stabilizedmuch sooner. Station 1 temperature 701 trended downwards for a period ofabout 500 seconds, down to about 256° C., but recovered and remained atthe set point during remaining of the wafer processing.

The data shows that with the temperature control scheme, showerheadtemperatures may be controlled to without about 4° C. within a 50 waferbatch. Because the data was generated without using feed forwardcontrol, implementation including feed forward control may improve theresponse to even less than about 4° C.

In another test, wafer-to-wafer results of deposition rate forTetraethylorthosilicate (TEOS) deposition were studied using a standardshowerhead and a temperature controlled showerhead in accordance withthe present invention. The standard showerhead does not include thetemperature controlled features of the present invention. It does notinclude the cooling mechanisms or the heater. In order to test theresponsiveness of the temperature controlled showerhead to changingconditions, 100 wafers were deposited with each showerhead under fourconditions. Before each condition, the process chamber was subjected toa remote plasma clean (RPC) where a plasma is ignited from gases fedinto a chamber that is located remotely from the processing chamber.Plasma-activated species from the RPC chamber then flow through adelivery line towards the processing chamber. Thus a RPC was conductedbefore wafers 1, 26, 51, and 76. In the first condition, TEOS wasdeposited for 12 seconds per wafer and thickness deposited weremeasured. In the second condition, after the RPC the showerhead wascooled with nitrogen gas from the reactant channel for 20 minutes. It isestimated that in the standard showerhead, after about 20 minutes offorced cooling with nitrogen gas the showerhead temperature reachedabout 240° C. In the third condition, the process chamber was idledovernight after the RPC. During this idle, the pedestal remains heatedto about 350° C., so that in the standard showerhead over this durationthe showerhead equilibrated to a temperature less than 350° C. In thefourth condition, after the RPC the showerhead was heated with a highpower plasma for 20 minutes. Nitrogen is used to generate this plasma ata flowrate of about 10 slm. The chamber pressure was maintained at about2.5 Torr and the high frequency power at about 1500 watts.

FIGS. 8A and 8B are plots of the thickness deposited in angstroms foreach wafer measured. Six wafers were measured for each condition.Regions 801 correspond to the first condition, discussed above. Afterthe RPC, the showerhead temperatures are elevated because exothermicreactions released energy at the showerhead surface. The standardshowerhead remained hotter for longer without additional cooling that ispossible in the temperature controlled showerhead, as shown by thethickness data. Note that TEOS deposition rate is higher at highershowerhead temperatures. After a few wafers, depositions at both thestandard showerhead and the temperature controlled showerhead decreased,then slowly increased. The temperature controlled showerhead maintaineda relatively stable deposition rate, but the deposition rate started todecrease again for the standard showerhead. It is believed that thesecond decrease in the standard showerhead station is attributed to theeffect of cold wafers entering the station, much like the temperaturedecrease shown on curve 102 of FIG. 1. The data shows that after a RPCsequence, the temperature controlled showerhead was able to equilibrateto a constant temperature, and hence a deposition rate, faster than thestandard showerhead.

Regions 802 correspond to the second condition. After the RPC sequencethe process chamber was cooled with nitrogen. In this region thedeposition with temperature controlled showerhead was affected lessinitially—there was less of a drop in deposition thickness than thestandard showerhead. Regions 803 correspond to the third condition.After overnight idling, the deposition with the temperature controlledshowerhead had the same characteristics as that after a RPC sequence.The deposition dips initially and regained relatively constant value.The deposition with the standard showerhead decreased over the initialwafers and also maintained a relatively constant value. Note thatalthough the deposition parameters are the same, the standard showerheadmaintained a lower deposition rate in region 803 than all the otherregions. Lastly, regions 804 correspond to the fourth condition. Highenergy plasma after the RPC sequence heated the showerhead to a highertemperature than RPC alone. In the standard showerhead, the highestdeposition rates were recorded in region 4. After an initial dip indeposition, the thickness appeared to equilibrate at a higher value. Inthe temperature controlled showerhead, the high energy plasma appearednot to affect the deposition, save perhaps for the very first wafer.

Overall, the range of thicknesses measured for the standard showerheadwas about 37 angstroms and for the temperature controlled showerhead,only about 13 angstroms. The wafer-to-wafer non-uniformity for thedeposition was 3.7% for the standard showerhead and 1.3% for thetemperature controlled showerhead. The better wafer-to-wafer uniformityfor the temperature controlled showerhead is a 66% improvement over thatof the standard showerhead.

Although various details have been omitted for clarity's sake, variousdesign alternatives may be implemented. Therefore, the present examplesare to be considered as illustrative and not restrictive, and theinvention is not to be limited to the details given herein, but may bemodified within the scope of the appended claims.

1. A temperature controlled showerhead for chemical vapor deposition(CVD), the showerhead comprising: (a) a stem comprising a convectivecooling fluid passageway; (b) a back plate thermally coupled to thestem; (c) a heater physically attached to the back plate; (d) a faceplate thermally coupled to the back plate; and (e) a temperature sensorfor measuring a temperature of the face plate.
 2. The showerhead ofclaim 1, wherein the temperature sensor is a thermocouple physicallyattached to the face plate, and further comprising a radio frequency(RF) filter electrically coupled to the thermocouple.
 3. The showerheadof claim 1, further comprising an RF filter electrically coupled to theheater.
 4. The showerhead of claim 2, wherein one or both of the heaterand the thermocouple are isolated from radio frequency power of definedfrequencies.
 5. The showerhead of claim 1, wherein the temperaturesensor is a pyrometer, fluorescence-based thermometer or infra-redthermometer.
 6. The showerhead of claim 1, wherein an external surfaceof the back plate comprises a coating to increase emissivity.
 7. Theshowerhead of claim 6, wherein the coating is anodized aluminum.
 8. Theshowerhead of claim 1, wherein the heater is embedded in the back plate.9. The showerhead of claim 1, wherein the convective cooling fluidpassageway is configured to flow clean dry air (CDA), argon, helium,nitrogen, hydrogen, or a mixture of these.
 10. The showerhead of claim9, wherein an inlet opening to the convective cooling fluid passagewayin the first showerhead stem is fluidly connected to a facilities CDA ata pressure of about 50-100 psi.
 11. The showerhead of claim 1, whereinthe face plate is attached removably to the back plate.
 12. Theshowerhead of claim 1, wherein the stem has a diameter of between about1.5 to 2.5 inches.
 13. The showerhead of claim 1, wherein the face plateand the back plate have a thickness of about 0.25 to 0.5 inches.
 14. Theshowerhead of claim 1, wherein the gap between the back plate and theface plate is about 0.5-1 inch.
 15. The showerhead of claim 1, whereinthe face plate has a diameter of about 13 inches.
 16. The showerhead ofclaim 2, further comprising a standoff between the back plate and theface plate through which the thermocouple is attached to the face plate.17. A temperature control system for controlling showerhead temperaturesin a CVD chamber, the system comprising: (a) a CVD chamber comprisingone or more temperature controlled showerheads, each showerheadcomprising; i. a stem comprising a convective cooling fluid passageway,ii. a back plate thermally coupled to the stem, iii. a face platethermally coupled to the back plate, and iv. a temperature sensor formeasuring the temperature of the face plate; (b) a cooling systemfluidly coupled to the convective cooling fluid passageways comprising:i. inlets and outlets to the convective cooling fluid passageways, ii. aliquid cooled heat exchanger configured to remove heat from a convectivecooling fluid that flows serially through the passageways of the onemore showerheads and is intermediately cooled by the heat exchanger, and(c) a controller coupled to the temperature sensor and a heater that isthermally coupled to the back plate.
 18. The system of claim 17, whereinthe controller is coupled to the temperature sensor and heater throughone or more RF filters and traps.
 19. The system of claim 17, whereinthe convective cooling fluid is discharged from the cooling system atambient pressure.
 20. The system of claim 17, wherein the convectivecooling fluid is selected from a group consisting of clean dry air(CDA), argon, helium, nitrogen, hydrogen, and a combination thereof. 21.The system of claim 20, wherein an inlet opening to the convectivecooling fluid passageway in the first showerhead stem is fluidlyconnected to a facilities CDA at a pressure of about 50-100 psi.
 22. Thesystem of claim 17, wherein the CVD chamber further comprises a chambertop with an inside surface coated with a high emissivity material. 23.The system of claim 17, wherein the liquid cooled heat exchangercomprises a cast metal block having embedded therein a cooling liquidline and a plurality of convective cooling fluid lines.
 24. Atemperature control system for controlling CVD showerhead temperature,the system comprising: (a) cooling means thermally coupled to theshowerhead; (b) heating means thermally coupled to the showerhead; (c)temperature sensing means thermally coupled a face of the showerhead;(d) RF filtering means electrically coupled to the temperature sensingmeans and heating means; and (e) controlling means for controllingtemperature.
 25. The system of claim 24, the cooling means furthercomprising; (a) radiative cooling means; (b) conductive cooling means;and (c) convective cooling means.